(MEN-stroo-WAY-shun)

The normal monthly shedding of blood and tissue from the lining of the uterus (womb) when pregnancy does not occur. During menstruation, menstrual blood and tissue flow from the uterus through the cervix and pass out of the body through the vagina. Menstruation usually occurs about every 28 days (except during pregnancy) and lasts 3 to 5 days, but this can vary from person to person. It normally starts during puberty and ends at menopause. Also called menses and menstrual period.